Method and apparatus for the casting of fusible materials



Oct. 6, 1964 H. A. FROMSON METHOD AND APPARATUS FOR THE CASTING OF FUSIBLE MATERIALS Filed Dec. 11, 1957 6 Sheets-Sheet 1 v I p l u INVENTOR How/1R0 A. FRO/450M BY cwmam ATTORNEY Oct. 6, 1964 H. A. FROMSON METHOD AND APPARATUS FOR THE CASTING 0F FUSIBLE MATERIALS Filed Dec. 11, 1957 6 Sheets-Sheet 2 INVENTOR HOWARDAFROMSON BY QM).

ATTORNEY Oct. 6, 1964 H. A. FROMSON METHOD AND APPARATUS FOR THE CASTING OF F'USIBLE MATERIALS Filed Dec. 11, 1957 6 Sheets-Sheet 5 INVENTOR HOWARD A. fROMSON Oct. 6, 1964 METHOD AND APPARATUS FOR THE CASTING OF FUSIBLE MATERIALS Filed Dec. 11, 1957 6 Sheets-Sheet 4 flfl 83 so 89 1 ea A I l 0; I /1 j Y a El I INVENTOR.

I HOWARD A. FROMSON ATTORNEY Oct. 6, 1964 H. A. FROMSON METHOD AND APPARATUS FOR THE CASTING OF FUSIBLE MATERIALS 6 Sheets-Sheet 5 Filed Dec. 11, 1957 INVENTOR. HOWARD AIROMSON ATTORNEY Oct. 6, 1964 H. A. FROMSON 3,151,

METHOD AND APPARATUS FOR THE CASTING OF FUSIBLE MATERIALS F iled Dec. 11, 1957 e Sheets-Sheet 6 I29 I29 F'IGJO I32 FIG. ll

INVENTOR.

HOWARD A FROMSON ATTORNEY United States Patent 3,151,366 METHOD AND APPARATUS FOR THE CASTING 0F FUSIBLE MATERIALS Howard A. Fromson, Weston, Conn. Filed Dec. 11, 1957, Ser. No. 737,176 18 Claims. (Cl. 22--57.2)

This invention relates to a method for the casting of fusible materials on a continuous or a discontinuous basis and to a mold for use in this method.

Fusible materials such as metals, glass and plastics have heretofore been cast by pouring them while in the molten state into molds which retain them in the desired form while their heat of fusion is removed to cause their solidification. The molds used for such casting have been made of various materials, but the materials used have had the common characteristic of remaining completely solid during the casting operation.

Now, in accordance with this invention I depart completely from this prior practice and cast fusible materials in contact with a retaining solid surface of a material which partially melts during the casting operation. This complete departure from prior casting practices provides major advantages both from the standpoint of the method for the casting of fusible materials and of the mold used in such casting.

Accordingly, it is an object of this invention to provide a method for the casting of fusible materials in which a mold surface is utilized which is readily renewed, and which in some embodiments of the method is renewed in each operation, whereby the remainder of the mold is protected from deterioration in extended use.

Another object is to provide a casting method in which a fusible material cannot pull away from the mold surface due to its own shrinkage and thereby lose thermal contact with the mold surface.

Another object is to provide a casting method in which the solidified casting, even when the fusible material is cast on the outside of the mold, for example, to form a hollow cylinder, can readily be removed from the mold.

Another object is to provide a casting mold which is simple in structure, and durable when used in this method.

A further object of this invention is to provide a method for the casting of fusible materials which does not require the use of special coating equipment for the casting mold, yet ensures the steady uniform removal of heat from the fused material being cast to produce castings having good internal structure.

Other objects of this invention, and the numerous advantages which it provides will become clearly apparent to those skilled in casting techniques from the detailed description of this invention which follows.

By the method of this invention, I bring a fused material into contact with a solid surface of a retaining material having a relatively low thermal conductivity and a melting point below the solidification temperature of the fused material, which is supported on the surface of a backing material having a higher thermal conductivity than that of the material forming the retaining surface, and solidify the fused material by withdrawing heat through the supporting surface of the backing material at a rate which prevents the complete fusion of the material which forms that surface.

By the use of the combination of a material of low thermal conductivity for the retaining surface and one of high thermal conductivity for backing material of the mold, I am able to keep the supporting surface of the backing material at a temperature below the melting points of the retaining material and of the backing material, and thereby am able to keep both a major portion of the re- 3 ,151,366 Patented Oct. 6, 1964 ice 2 taining material and all of the backing material at tem'= peratures considerably below that of the fused material and below their own melting points.

In carrying out this method, I may keep the retaining material below its own melting point, as well as below the solidification temperature of the material being cast, by the absorption of heat from the retaining material by a backing material which has a high thermal conductivity and a high capacity to absorb heat and is present in an amount which has a total capacity to absorb the heat of fusion of the material being cast and any super-heat carried by that material, while maintaining its supporting surface below the melting point of the retaining material and below its own melting point. In this embodiment of my method, I do not utilize a circulating coolant to withdraw heat from the backing material.

Alternatively, I may afiirmatively withdraw heat from the backing solid by the use of a circulating coolant at a rate which keeps its supporting surface below the melting points of the retaining material and below its own melting point, rather than relying entirely upon the heat capacity of the backing solid to absorb the heat of fusion and any super-heat carried by the material being cast.

In each of these alternative embodiments of my method, the relatively low temperature at which the supporting surface of the backing material is maintained, prevents the complete fusion of a thin layer or skin of the retaining material directly adjacent the surface of the backing material during the casting operation.

In carrying out this method, I merely bring the fused material into contact with the retaining surface of the mold and permit the supporting material of the mold to absorb heat from the fused material through the solid layer of retaining material until at least the outer portions of the material being cast have solidified, and then remove the partially, or completely, solidified material from contact with the retaining surface of the mold. In general, I prefer to completely solidify the casting of the fusible material which is in contact with the mold surface to avoid the problems involved in handling a casting which is superficially solidified, but which has a still molten interior.

In this casting operation, the surface of the retaining material in contact with the fused material being cast is usually heated above its melting point, at least at the beginning of the operation, with the result that a surface layer of the retaining material melts. This superficial melting of the retaining material is highly advantageous and is, I believe, an important factor contributing to the advantageous features provided by this invention. However, it is essential that a thin, solid layer or skin of the retaining material be present on the surface of the backing material at all times during the casting operation.

The mold in accordance with this invention, comprises a combination of a retaining solid and a backing solid. The retaining solid forms the surface with which the fused material being cast comes into contact. It has a relatively low thermal conductivity, a melting point below that of the fusible material being cast, and is immiscible with the fused material being cast when it is itself in a fused state. The backing solid which provides a supporting surface for the retaining solid is one which is capable of absorbing the heat of fusion of the fused material being cast, and any super-heat which it may carry with or without the assistance of a circulating coolant, without permitting the temperature of the retaining solid to rise to a point such that it is completely fused during the casting operation.

The mold in accordance with this invention may comprise a backing solid having a high capacity to absorb heat, as well as high thermal conductivity, which is present in an amount which has the capacity to absorb the total heat of fusion of the material being cast together with any super-heat carried thereby, while maintaining its supporting surface in contact with the retaining material, below the melting point of the-retaining material. This form of my mold has no provision for forced cooling, as by means of a circulating coolant, although in some modifications the backing solid may lose some heat by radiation or by conduction to its surrounding environment. For brevity this form of my mold will be referred to hereinafter as a massive mold.

An alternative form of this mold is provided with means for the forced cooling of its backing solid, which is a ma= terial of higher thermal conductivity than the material which forms the retaining material of the mold. It may, but need not be, a material of high heat capacity. This forced cooling capacity of the backing solid of this alternative form of my mold must be adequate to remove heat from the backing solid at a rate which keeps its supporting surface below its own melting point and below that of the retaining material carried by its supporting surface. The means for the forced cooling of the backing solid of this mold may be a coolant liquid circulated through channels within the body structure of the backing solid. This alternative form of my mold is referred to hereinafter as the fluid-cooled mold.

The mold in accordance with this invention, may take many different specific forms. It may be adapted for the casting of a fusible material in contact with its inner surface, or alternatively it may be adaptedfor the casting of a fusible material around its outer surfaces. However, in each of numerous embodiments of the casting mold which may be used, the material hereinbefore termed the retaining solid forms the surface with which the fused material comes into contact and which determines the form of a surface of the final casting. Thus, when the fusible material is cast within the mold, the retaining solid forms the inner surface of the mold, while the material termed the backing solid forms the outer part of the mold. 011 the other hand, when the fusible material is cast around the outer surface of the mold, the retaining surface is on the outer surface of the mold.

The essential characteristics of the backing solid of this mold are physical strength, a thermal conductivity which is materially higher than that of the retaining solid which it supports, and chemical non-reactivity with respect to the retaining solid. The backing solid may, like the retaining solid, have a melting point lower than that of the fusible material which is cast in the mold. However, the melting point of the backing material need not be lower than that of the fusible material which is cast in the mold, whereas it is essential that the retaining material have such a lower melting point to secure the major advantages provided by this invention. In the alternative form of my mold in which no provision is made for the forced cooling of the backing solid, it also must have the capacity to absorb heat at a relatively high rate and be present in an amount such that its total heat capacity is sufficient to absorb the superheat and at least a substantial portion of the heat of fusion of the material being cast.

Any solid material having high thermal conductivity and reasonably good structural strength is suitable for use as the backing solid for my mold. The structural metals are generally suitable for use as the backing solid of the alternative form of my mold which is provided with means for forced cooling. In the form of my mold which includes no means for forced cooling the particulaf metal used must be selected in view of the thermodynamic characteristics of the fusible material which is cast in the mold and of the casting operation itself. Copper, the various alloys of copper, aluminum and aluminum alloys, silver and silver alloys are particularly suitable for this purpose because of their relatively high thermal conductivity, high capacity to absorb heat, and good structural characteristics. Graphite is also a suitable material for the backing solid of the mold and can be used even in the casting of steel, since the retaining material prevents the steel from picking up the graphite. In general, I have found that copper and its various alloys are widely useful as the backing solid of my mold.

The particular material which I use to form the retaining surface of the mold in this method is determined by the characteristics of the fused material which is to be cast. As will be appreciated from the foregoing, the retaining material must have the following essential characteristics:

(1) A solidification temperature lower than that of the material being cast,

(2) A thermal conductivity which is low relative tothe thermal conductivity of the backing material of the mold,

(3) Immiscibility, when in the fused state, with the material being cast,

(4) Non-volatility or low volatility at the maximum temperature to which it is heated during the casting operation, and

(5) Chemical non-reactivity with the material being cast and with the backing solid.

I have found that inorganic salts, mixtures of inorganic salts, inorganic oxides and mixtures of inorganic oxides are generally suitable materials from which to select a satisfactory material for the formation of the retaining surface of my mold for the casting of the usual fusible matenals. Examples of salts which I may use are:

Melting Boiling Point, Point, Specific Degree Degree Gravity Centigrade Centigrade Barium Chloride 925 1, 560 3. 856 Barium Fluoride. 1, 280 2, 137 4. 83 Cadmium Fluoride... 1, 100 1,758 6. 64 Calcium Chloride. 772 1, 600 2. 512 Copper Chloride 422 1, 366 3. 53 Lead Chl0ride- 501 950 5. 85 Lead Fluoride-. 855 1, 290 8. 24 Lithium Bromide- 547 1, 265 3. 464 Lithium Chloride 613 l, 353 2. 068 Magnesium Chloride 708 1, 412 2. 316 Magnesium Fluoride. l, 396 2, 239 2. 9-3. 2 Potassium Bromide. 730 1, 380 2. 75 Potassium Chloride. 776 1, 500 1. 984 Potassium Fluoride 880 1, 500 2. 48 Silicon Oxide 1, 710 2, 230 2. 32 Silver Chloride 455 1, 550 5. 56 Sodium Chloride 801 1, 413 2.165 Sodium Cyanide 563. 7 1, 496

As noted hereinbefore, in carrying out the casting operation in accordance with this invention, it is desirable to have the surface of the retaining material, which is in. contact with the fusible material being cast, superficially melted, but it is essential that the retaining layer of the mold not be permitted to completely fuse at any time during a given casting operation. A solid layer or film of the retaining material must be kept on the surface of the backing material of the mold throughout each casting operation. Therefore, the melting point of the retaining material determines the maximum temperature to which the mold can rise during the casting operation.

The rate at which heat is withdrawn from the layer of retaining material of the mold, as compared with the rate at which heat passes from the fused material being cast into the retaining layer, determines Whether or not the entire thickness of the retaining layer of the mold can reach or exceed its melting point during a casting operation. The rate at which heat passes into the layer of retaining material is determined by the weight of the fusible material which is being cast and upon its thermodynamic characteristics. The rate at which heat passes from the layer of the retaining material to the backing material of the embodiment of my mold in which the backing material is cooled by a circulating coolant is determined by the rate at which heat is delivered to the mold, by the thermal conductivity of the retaining layer and by the thermal conductivity, thickness and mechanism of cooling of the backing material; In steady operation in which no part of the mold is changing temperature, this mold acts only to transfer heat by conduction from the cast metal to the cooling medium. However, from a practical standpoint, even the fluid cooled mold designed for continuous casting, must have the capacity to withstand the sudden transient heating which occurs when liquid metal is brought into contact with the retaining surface, without complete fusion of the retaining layer at any point. This capacity is a property of the metal of which the mold is made, and of the initial temperature of the mold, and has nothing to do with the nature and extent of the fluid cooling. In the alternative embodiment of my mold in which no circulating coolant is used, the rate at which heat passes from the layer of retaining material to the backing material of the mold depends upon the weight of the backing material present and its thermodynamic characteristics.

As will be appreciated from the foregoing discussion, the common and essential requirement in the use of the alternative forms of my mold is that the retaining material, with its melting point below the solidification temperature of the material being cast, must be adequately cooled by the backing material so that the temperature of the interface between the retaining material and the supporting surface of the backing material never, for any reason approaches the melting point of the retaining material. In carrying out this method I have found that I am able to meet this common and essential requirement by correlating the thermodynamic characteristics required of the mold with the thermodynamic characteristics of the fusible material being cast in each operation, by the use of five thermodynamic equations which are given hereinafter.

Of the five equations given hereinafter, Equations I, II and HI apply to the use of the massive mold in a casting operation, while Equations I, II, IV and V apply to the use of a fluid-cooled mold. Stated in another way, I have found in the use of a massive mold in a given casting operation, that when the requirements of Equations I, II and III are met, the solid layer of the retaining material is maintained on the supporting surface of the mold at all times, and the casting operation is successful. Similarly, in the use of a fluid-cooled mold in a given casting opertaion, I have found that when the requirements of Equations I, II, IV and V are met, that a solid layer of retaining material is maintained on the supporting surface of the mold at all times and the casting operation is successful.

The thermodynamics requirements for a massive mold in a given casting operation will first be considered and exemplified with reference to Equations I, H and III. As already noted hereinbefore, a fluid-cooled mold must have the thermal capacity to withstand sudden transient heating which occurs when a fused material is brought into contact with its retaining surface, without complete fusion of the retaining layer at any point. For this reason, the fluid-cooled mold, like the massive mold, must meet the requirements of Equations I and II. The description of the application of Equations I and II to a massive mold apply with equal force to their application to a fluidcooled mold. Equations IV and V apply only to a fluidcooled mold and they are discussed and their application to a fluid-cooled mold specifically exemplified following the discussion of the thermodynamics of the massive mold.

In the casting of any given quantity of a fusible material, the maximum temperature reached by the massive mold is determined by its own heat absorbing capacity, as well as by the amount of super-heat carried by the fused material at the time it is brought into contact with the retaining surface of the mold, and the thermodynamic characteristics of the fused material. The heat absorbing capacity of the massive mold, as a whole, is for practical purposes, that of its backing material, and is determined by the amount of the backing material present and its thermodynamic characteristics. The heat absorbing ca- 6 pacity of the backing material of the massive mold is its thermal conductivity, multiplied by its density and by its specific heat, which may be expressed as:

KpC' in which:

K=thermal conductivity in B.t.u. per foot per hour in degrees Fahrenheit. p=density in pounds per cubic foot. C =specific heat in B.t.u. per pound in degrees Fahrenbelt.

The heat capacity required in the massive mold is determined by the amount of the fusible material which is being cast in each operation, the melting point of the fusible material, the amount of super-heat which it carries upon its initial contact with the retaining surface of the mold, and its physical and thermodynamic characteristics. Therefore, I determine the quantity of the backing material which is required for a given casting operation in terms of its own thermodynamic properties, the quan tity of the fusible material being cast, the thermodynamic characteristics of the fusible material being cast and the thermodynamics of the casting operation itself.

By the use of Equations I and II given below, I determine the heat absorbing capacity which is required of my massive mold for a given casting operation, to give a pre determined, maximum, initial temperature for the mold at the beginning of each casting operation and a predetermined, maximum temperature during the particular castting operation with which I am concerned. As already noted, the maximum temperature which I can permit the mold to reach in this method must be below the melting point of the retaining material of the mold, and I prefer to have it well below that temperature to provide a factor of safety to compensate for unexpected super-heat in the fused material being cast, turbulence in the mold when the fused material is poured and other disturbing infiuences which may enter into the casting operation. I have found that, in routine casting operations, it is desirable to keep the maximum temperature of the backing material of the mold at least 250 F. below the melting point of the retaining material, in the casting of materials, such as, for example, steel and copper, which have relatively high melting points. This temperature differential of 250 F. provides a safety factor which more than compensates for the loss in thermodynamic efficiency involved in narrowing the temperature ranges utilized. In the casting of fusible materials which melt at considerably lower temperatures than, for example, steel a smaller safety factor, i.e. a smaller temperature differential, is entirely adequate.

It is desirable, but not essential, to use a massive mold which can be used at a relatively high initial temperature, since such a mold does not require complete cooling be tween successive casting operations. In general, I have found that it is desirable in the practical use of this invention to utilize as my mold a combination of a retaining material and a backing material in any given casting operation, which permits the use of a mold temperature at the beginning of the casting operation which is substantially above ambient temperatures. As can well be appreciated, the higher the permissible initial mold temperature, the less time must be spent between successive casting operations, and, hence, the more efficient the operations involved.

After determining the heat absorbing capacity required of my massive mold for the particular casting operation involved by the use of Equations I and II, I then determine the quantity of the backing material which I must include in the mold to cause it to operate within the desired temperature range by the use of Equation III.

=ne erf n In this equation:

T =melting point of fusible material being cast in degrees Fahrenheit.

T =highest temperature which the retaining material is to reach.

C ,=the specific heat of the fusible material being cast when it is in the solid phase, expressed in B.t.u. per pound in degrees Fahrenheit.

H=heat of fusion of the material being cast in B.t.u.

per pound.

erf=error function.

e=2.7l8 (the base of Naperian logarithms) n=the parameter relating Equation I to Equation 11 Equations I and II are parametric equations which are related by the parameter n. Equation I is solved to determine the value of n which is then substituted in Equation II to determine the value of K C Equation I is transcendental as to 22, since n" can be evaluated only by a trial and error procedure. In the solution of this equation the numerical value of the lefthand side of the equation is determined by the substitution of the numerical values of the terms of that side of the equation which apply to the contemplated casting operation. To determine the value of n which will give the product:

2 ne art 11.

equal to the numerical value of the left-hand side of the equation, a value of n is arbitrarily selected and the value of the product determined. If this product is larger than that of the left-hand side of the equation, another trial value for n is selected and the process repeated. This process is repeated until a value for n is found which gives a product equal to that of the left-hand side of the equation.

The erf or error function of a given number is a tabulated factor which is to be found in reference tables. Tables of error functions may be found, for example, in the reference entitled Transcendental Functions by Flugge or in Heat Conduction by Inger-sol and Zobel. In the solution of Equation I, the error function corresponding to the trial value selected for n must be used.

To illustrate the solution of Equation I as applied to a specific set of casting conditions, the casting of copper may be selected in an operation in which the terms on the lefthand side of Equation I have the following numerical values:

the product ne erf n determined. This process is repeated using different values for it until a value for 11" is found which gives a product of 0.141. The product obtained with three ditferent values of n are as follows:

Trial Value Product we erf n Of'IL n e erfn Thus, for the selected conditions for the casting of copper the correct value for n for use in the solution of Equation II is 0.34.

EQUATION II T ,,=the initial temperature of the mold in degrees Fahrenheit.

K'=the thermal conductivity of the fusible material being cast, when it is in the solid phase, expressed in B.t.u. per foot, per hour in degrees Fahrenheit.

p =the density of the fusible material being cast in pounds per cubic foot.

K, p and C have the same significance as in the formulae given hereinbefore for the heat absorbing capacity of the backing material of the mold.

EQUATION III W 'D( S O) m D m e)+H In this equation:

W =weight of the casting of the fusible material being made in mold. W =weight of the supporting material.

The remaining characters in this equation have the same significance as in Equations I and II.

Equations I and II are, in effect, a single equation since they are tied together by the numerical factor n. The solution of Equation I to determine the value of n for a given combination of a fusible material, a retaining material and a backing material, permits the use of Equation H for the determination of the feasibility of using the particular combination, and for determining the conditions under which the casting operation can be carried out.

The applications of Equations I, II and III in the method in accordance with this invention, are specifically illustrated by the examples given below. In these examples, the particular molds selected for consideration utilize barium chloride as a retaining material with copper and steel, respectively, as backing materials. Copper and steel are the fusible materials selected for the purposes of illustration. These examples specifically illustrate the use of Equations I and II for determining the feasibility of each of these four combinations of materials in a casting operation, and the thermal conditions which may be used in the casting operation. They also illustrate the use of Equation III for determining the weight of a casting which can be produced in a particular mold.

The solution of Equation I gives values for n of 0.66 for the casting of steel and of 0.34 for the casting of copper, under conditions such that the surface temperature of the supporting material does not exceed 1,760 F. The values for the other characters of Equation II, which are characteristic of the mold support, are as follows:

Cast Steel Cast Copper Mold Mold Backing Backing The values for the characters of Equation II, for the material being cast, are as follows:

Steel Copper K in B.t.u./ft./hr., F 20 200 p in 10.0w 400 550 o, in Btu/lb 0. 15 0.10

Example 1 The use of Equations I and H to determine the heat absorbing capacity required in a massive mold for carrying out a given casting operation, may be illustrated by an operation in which steel is cast into a mold which has a barium chloride retaining surface and is to be cooled to 100 F. after each casting operation, and the mold temperature is permitted to rise to the melting point of the barium chloride retaining layer (1,760 F.) in each casting operation. These conditions are extreme, since it is generally impractical to cool the mold to 100 F. and the permissible maximum temperature of 1,7 60 F. provides no safety factor for the operation. Substituting the appropirate constants in Equation II, reduces that equation w Kip! OD! 100- 1,760 1,446 KPCD Kip! C1D! Since 'C =l,380, K C must exceed 1,045. K C

for copper is 11,000, so it is well within the usable range. K C for steel is 1,380 and is barely within the range of operability with no safety factor in the operation, when a relatively low initial mold temperature is used. Steel is therefore impractical for use as a backing material for a mold to be used for the casting of steel.

Example 2 The inclusion of a safety factor in the computation of Example 1, by restricting the maximum temperature to which the backing material of the mold can rise to 1,500 F. (T 1,500) to provide a differential of 260 F. between that temperature and the melting point of the barium chloride retaining layer of the mold, reduces Equation II to the following:

M lli 100 1,500 1,714 KPOD KPCD=2,03O

Therefore, steel with a K C of 1,380 cannot be safely used as a supporting material for a mold for the casting of steel, even when using the relatively low initial mold temperature of 100 F. This result confirms the conclusion to be drawn from Example 1.

Example 3 KpC =5,000

Therefore, for the casting of copper, the heat absorbing capacity of the mold support K C must exceed 5,000. Steel with its K C of 1,380 is not suitable for use as a supporting material for the mold to be used for this operation, while copper itself, with a K C of 11,000, is entirely suitable.

Example 4 To determine the quantity of copper which must be used as a mold support in a massive mold for use in the casting Such substitution gives the ratio of Thus, 0.45 pound of steel may be cast in the mold for each pound of copper used as a supporting material for the mold, when no heat whatever is lost from the mold support by radiation or air cooling. In the case of an ingot mold consisting of a copper backing in the form of a shell coated on its interior surfaces with a retaining material such as barium chloride, heat is lost by radiation from the outer surfaces of the copper shell and will permit the casting of as much as one pound of steel for each pound of copper contained in the supporting shell.

Example 5 The initial temperature which a massive mold may have when it comes into contact with the fused material to be cast, without the retaining material exceeding its melting point i indicative of the usefulness of the mold in the particular casting operation in question and gives the temperature to which the mold must be cooled between successive casting operations. This example illustrates the application of Equations I and II to the casting of steel in a mold which has copper as a backing material. Upon the substitution of the values for a mold having copper as a backing material for a casting operation in which molten steel is the fusible material being cast, including the value of 0.34 for n obtained by the solution of Equation I, and using a value of 1,760 for T Equation II becomes:

T, cannot exceed 1,760" F. since this is the melting point of barium chloride. Thus, according to Equation II, the temperature of the copper mold support at the beginning of the casting operation cannot exceed 1,560 F., if the maximum temperature reached by the supporting copper of the mold is not to exceed the melting point of the barium chloride used as a retaining material in the mold.

Example 6 The use of a value of T of 1,760 in Example 5, for a mold having a barium chloride retaining surface provides no margin of safety in the use of the massive mold. The maximum temperature of the retaining layer of barium chloride, preferably, should not exceed 1,500 P. to provide a reasonable margin of safety in the use of the mold. Upon the substitution of 1,500 for T and the other values given hereinbefore for the casting of steel, using a mold having copper as a backing material, Equation II becomes:

Thus, it is desirable for the initial temperature of the copper mold support not to exceed 893 F., to maintain an adequate margin of safety which precludes the possibility of melting through the barium chloride retaining layer of the mold.

Example 7 The application of Equations I and II to the casting copper may be illustrated in connection with the use of a massive mold having a retaining surface of barium chloride and a copper backing by a determination of the max-. imum initial temperature of the mold which may be used in the casting operation without exceeding the melting point of barium chloride, i.e. without utilizing any factor of safety in the operation. A substitution of the values given hereinbefore for the casting of copper in a mold using copper as a backing material reduces Equation II to the following:

This relatively high permissible maximum initial temperature for the mold shows the feasibility of such a casting operation.

Example 8 The casting operation illustrated by Example 7, includes no safety factor. As a practical matter, the retaining layer of barium chloride should not be allowed to exceed about 1,500 F., duringthe casting operation. The maximum permissible temperature when casting copper, using a massive mold having a barium chloride retaining layer which is not permitted to exceed 1,500 F. during the casting operation, can be obtained by a substitution in Equation II of 1,500 for T along with the other appropriate values given hereinbefore. Such substitution reduces Equation II to the following:

Thus, the casting operation may be carried out with an adequate factor of safety, while cooling the mold only below 557 F. between casting operations.

Of the foregoing, Examples 1, 2 and 3, illustrate the use of Equations 1 and II for the determination of the suitability or unsuitability of a given material for use as a backing material in a massive mold intended for use in a particular casting operation. As shown by these examples, copper is suitable for use as a backing material in a mold using barium chloride as a retaining material for the casting of both steel and of copper itself.

On the other hand, steel is barely operable as a backing material in a massive mold using barium chloride as a retaining material, for use in the casting of steel, as shown by Example 1. However, it is clear from that example that such a mold would not be particularly suitable in commercial operations, since it would have to be cooled well below 100 F. for each successive casting operation and care otherwise exercised to avoid melting entirely through the barium chloride retaining layer during the casting operation. As shown by Example 3, steel cannot be used as a backing material in a mold to be used for the casting of copper.

As shown by Example 4, a massive mold for the casting of steel should include at least 2.2 pounds of copper for each pound of steel cast by the use of the barium chloride copper mold, in an operation in which no heat is lost from the mold by radiation.

Examples 5-8, inclusive, illustrate the use of Equations I and II for the determination of the temperature below which a barium chloride-copper massive mold must be cooled in the casting of steel and copper respectively. As shown by Example 5, the mold can be used at the high initial temperature of 1,560 F. in the casting of steel when no safety factor is included in the operation. More important is the fact shown by Example 6, that the mold need only be cooled to 893 F. while including a safety factor which is entirely adequate to preclude any danger of entirely melting the retaining layer of barium chloride.

As shown by Examples 7 and 8, a barium chloridecopper massive mold must be cooled between casting operations to a somewhat lower temperature in the casting of copper than in the casting of steel. However, as shown by Example 8, the mold need only be cooled below 557 F. to include an adequate factor of safety in the operation to avoid a melt-through of the barium chloride retaining layer.

In the foregoing examples, the use of barium chloride-copper and barium chloride-steel massive molds, respectively, for the casting of copper and steel, respectively, is solely for the purpose of fully illustrating this embodiment of the invention, and it will be fully understood that the invention is by no means limited to these particular combinations. The casting of steel and copper were chosen for illustrating the invention for the reason that both are recognized to be difficult casting operations. Steel is difficult because of its high melting point, while copper is even more difficult due to its high heat capacity. While, as brought out by these examples, a barium chloride-steel mold is barely operable for the casting of steel and is inoperable for the casting of copper, such a mold is entirely suitable for the casting of many less difiicult fusible materials.

The thermodynamics of the fluid-cooled mold will now be considered and exemplified. The use of a fluid-cooled mold for a single-casting is governed by the foregoing Equations I and II. When such a mold is used for continuous or for semi-continuous casting, the thermodynamics involved must fulfil the requirements of Equations I and II, but also must meet the requirements of Equations IV and V. In the application of Equations I and II to a fluid-cooled mold, the various symbols of those equations have the same meaning as when applied to a massive mold with the single exception of T which is defined as follows for application to a fluid-cooled mold:

T =temperature of the surface of the backing material from which heat is withdrawal by a coolant.

Equations IV and V, apply to the functioning of a fluid-cooled mold as a continuous conductor of heat from the fusible material being cast to the fluid cooling medium. These equations are as follows:

K=the thermal conductivity of the backing material of the mold in B.t.u. per foot per hour in degrees Fahrenheit.

The remaining symbols in these equations have the following meanings:

T =the melting point of the retaining material of the fluid-cooled mold.

T,=the temperature of the surface of the backing material which carries the retaining material of the fluidcooled mold.

F=rate of heat flow per unit area in B.t.u. per square foot per hour from the fusible material to the fluid cooling medium.

t=thickness of the layer of the retaining material in feet.

K =thermal conductivity of the retaining material in B.t.u. per foot per hour per degrees Fahrenheit.

L=thickness of the backing material in feet between its surface carrying a retaining material and its surface from which heat is withdrawn by a coolant.

When Equations IV and V are applied to a fluid-cooled mold used in intermittent or semi-continuous casting, the terms F, t, and T must be regarded as average values, since each of these quantities fluctuate during such castmg.

It will be noted that Equations IV and V do not take into account the specific heat of the backing material or of the retaining material of the fluid-cooled mold, and are concerned only with the thermal behavior of the mold in the transfer of heat by conduction from the fused material being cast to the fluid coolant. Since the mold functions entirely as a continuous conductor, not as a heat absorber as in the case of the massive mold, no specific heat term is required by either Equation IV 01' Equation V.

The application of Equations IV and V to a procedure in accordance with this invention utilizing a fluid-cooled mold for the casting of a steel slab is illustrated by Example 9 which follows.

Example 9 A steel slab having a thickness of one inch weighing 40 pounds per square foot is cast continuously at the rate of one square foot per minute in a mold comprising a refractory container, the bottom of which is formed by a copper slab 0.25 foot thick, the lower surface of which is water-cooled to maintain its temperature at 260 F. and the upper surface of which carries a solid layer of barium chloride, on which is superimposed fused barium chloride maintained approximately at its melting point of 1760 F. In this operation the molten steel is solidified in a layer moving across the surface of the solid barium chloride and under the fused barium chloride by the withdrawal of heat from the copper slab. During the steady operation of this casting procedure the only heat furnished to the mold was carried by the molten steel. This mold is substantially identical to that described hereinafter with reference to FIGURES 2 and 3, except in that the entire lower surface of the copper slab is watercooled, instead of being provided with conduits within the slab for the circulation of a coolant. In this mold the solid layer of barium chloride functions as the retaining solid, while the copper slab acts as the backing solid. During the casting operation the steel is blanketed from atmospheric oxidation by the lower specific gravity, fused barium chloride covering its upper surface. Taking the thermal conductivity of solid barium chloride as 1.0 B.t.u./ft./hr./ F., the thermal conductivity of copper is 220 B.t.u./ft./hr./ F. and the heat of fusion of the steel being cast as 120 B.t.u. per lb. and substituting these numerical values in Equation IV, we obtain the following equation:

t= 0.00l14 (Equation IVA) The rate of heat flow from the solidifying steel slab to the water-cooled surface of the copper slab when operating at a casting rate of one square foot per minute was 288,000 B.t.u. per square foot per hour. The substitution of this value in Equation IV-A gives:

t=0.004 foot m quation V 14 When the layer of solid barium chloride is & inch thick the temperature of the surface of the copper carrying the solid barium chloride, according to Equation V-A, is only 590 F. or well below the melting point of the copper (1981 F.).

The conditions of operation utilized in Example 9, give rise to a relatively severe heat input into the mold. A reduction of this heat input to one-fourth of that of Example 9, will cause an increase in the thickness (t) of the solid barium chloride layer to less than inch, but a decrease in the temperature of the surface of the copper which carries the solid layer of barium chloride (T to 340 F. Thus, this mold system is inherently quite stable, since the thickness of the solid layer of barium chloride which protects the surface of the copper is relatively insensitive to varying thermodynamic conditions in the operation.

In operating as described by Example 9, some of the solid barium chloride is melted when it is initially contacted by hot steel. However, it is thermodynamically impossible for the barium chloride layer to completely melt if the initial pouring temperature is not permit-ted to exceed about 2000 F.

The details of the method in accordance with this invention and the details of the mold utilized in carrying out the method can be widely varied. The casting can be carried out batchwise by a procedure in which the casting is formed within the mold or by one in which it is formed around the mold. It may be carried out by a continuous procedure in which the casting travels horizontally, in a downwardly vertical direction or in an upwardly vertical direction. The detailed form of the mold utilized will, of course, depend upon the particular procedure utilized.

Specific embodiments of both the method and the mold of this invention Will be described with reference to the accompanying drawings in which like reference characters are used to refer to like parts. In the drawings:

FIGURE 1 is a cross-sectional view of a simple form of the fluid-cooled mold in accordance with this invention which is adapted for use in a discontinuous casting operation by the method of this invention.

FIGURE 2 is a cross-sectional longitudinal elevation of a fluid-cooled mold in accordance with this invention which is adapted for one continuous, horizontal casting of a slab of a fusible material by this method.

FIGURE 3 is a cross-sectional View taken along the section line 33 of FIGURE 2.

FIGURE 4 is a cross-sectional longitudinal elevation of an alternative embodiment of a fluid-cooled mold which is adapted for the continuous horizontal casting of a slab of a fusible material.

FIGURE 5 is a diagrammatic, elevational view in partial cross-section of a fluid-cooled apparatus in which I continuously cast a fusible material in an upwardly direction.

FIGURE 6 is a diagrammatic view, in partial crosssection, of a fluid-cooled apparatus for the casting of fusible material on the outside of a mold to produce a seamless tube or a seamless tube blank adapted for elongation into a seamless tube.

FIGURE 7 is a diagrammatic view, in partial crossseotion, of an alternative form of apparatus adapted for the casting of a seamless tube or tube-blank, and

FIGURE 8 is a diagrammatic view, in partial crosssection, of apparatus adapted for the continuous casting of a flexible sheet of a fusible material.

FIGURE 9 is a cross-sectional view of a simple form of the massive mold, in accordance with this invention, adapted for the casting of solid bodies of a fusible material.

FIGURE 10 is a diagrammatic cross-sectional view illustrating the application of the method in accordance with this invention, utilizing a massive mold for the production of tubular castings of a fusible material.

FIGURE 11, is a cross-sectional view of the massive mold used in the embodiment of my method illustrated by FIGURE 10, shown on a larger scale than by FIG- URE 10, after a cylinder of a fusible material has been deposited upon it by the casting operation illustrated by FIGURE 10.

In describing the apparatus illustrated by these drawings, barium chloride will be used as an example of the retaining material, and copper as an example of the backing material of the mold. In describing the method these materials will be used as illustrative of the mold materials, and steel is selected as an example of the fusible material which is cast. These specific materials are used in describing the mold as illustrated by the drawings and in describing the use of the molds, solely for the purpose of simplifying the description and, as will be understood from the foregoing discussion of the invention, there are numerous materials which are entirely suitable for use as alternatives for each of these materials.

Referring specifically to FIGURE 1, the numeral 1 designates a copper container which carries on its inside surfaces a layer 2 of solid barium chloride between the tray and the steel ingot 3 within the tray. The nozzles 44 are positioned adjacent the sides and bottom of the tray 1 and adapted to direct a spray of water on the adjacent portions of the outside of the tray, from the conduit 5 which is connected to a suitable source of cooling water.

In carrying out the method in accordance with this invention by the use of the simple mold illustrated by FIGURE 1, I first introduce molten barium chloride into the copper container 1, solidify the barium chloride on the bottom and side surfaces of the inside of the container and pour ofl? any excess molten barium chloride, to form a layer of solidified barium chloride which is preferably slightly thicker than the layer 2 of solid barium chloride forming a part of the mold as the ingot 3 is actually solidified. I then pour molten steel into this copper-barium chloride mold, while spraying water on to its outside surfaces from the nozzles 44 to cool the copper and to cause it to withdraw heat from the molten steel through the intermediate layer of solid barium chloride, to produce the steel ingot 3.

After the steel ingot 3 has entirely solidified, and while it is still at a temperature above the melting point of barium chloride, the casting may be removed from the mold. Alternatively, the mold and its contents may be permitted to cool and then be reheated above the melting point of the barium chloride retaining layer. In either case, the melting of the barium chloride frees the ingot and permits it to be readily removed from the mold.

In carrying out this molding procedure, the thickness of the layer 2 of solid barium chloride which forms an essential part of the mold is automatically adjusted by the thermal characteristics of the system. Any excess barium chloride which is initially placed on the inside of the copper container is fused by heat from the molten steel and, by virtue of the fact that its specific gravity is lower than that of steel, the excess barium chloride which is fused is forced to the surface of the steel, leaving the solid layer of barium chloride of automatically adjusted thickness on the inside surfaces of the copper container. The fused surface layer of barium chloride protects the steel from atmospheric oxidation.

The more complex mold illustrated by FIGURES 2 I and 3 operates on exactly the same basic principles as the simple mold shown by FIGURE 1. Referring specifically to those figures, it will be seen that the mold there illustrated consists of a tank 10, of a refractory material, the bottom of which carries a copper slab 11, the upper surface of which forms a horozontal trough 12, which extends the length of the tank 10. The trough 12 carries carries a molten layer of barium chloride 16 above the steel slab 14, which protects the steel from atmospheric oxidation and provides a continuing source for barium chloride for the layer 13 of solid barium chloride. A suitable source of heat may, if desired, be provided for the molten barium chloride 16, such as, for example. electrical resistance heaters.

Referring particularly to FIGURE 2, it will be seen that one end of the tank 10 is provided with an inlet conduit 17 for a fused material, provided with an adjustable gate valve 18 by which the rate of flow of a fused material can be adjusted or terminated, a lateral header 19 which causes the molten steel flowing from the inlet conduit 17 to flow laterally and enter the end of the trough 12 as a layer of substantially uniform thickness extending entirely across its width, to form the slab 14. The opposite or outlet end of the tank 10 is provided with an exit die 20, which is adapted to reduce the thickness of a hot but now solidified slab of steel as it is pulled through the die by the action of the traction rolls 21-21 and to form a seal against any leakage of the molten barium chloride from the tank 10. The conduit 22 provides an inlet for the introduction of a molten barium chloride into the tank 10.

In starting a continuous casting of molten steel by the use of the apparatus illustrated by FIGURES 2 and 3, a hot dummy plug is inserted in the orifice of the exit die 20. This plug is provided with a slablike extension which is positioned between the traction rolls 21-21. Molten barium chloride is then introduced into the tank 10 through the conduit 22 while the copper slab 11 is cooled by the circulation of a cooling fluid through the passageways 1515 to cause a layer of solid barium chloride to solidify on its surface. The fused steel flows from conduit 17 into the header l9 and along the trough 12. The molten steel displaces the molten barium chloride but flows over the solid barium chloride deposited on the copper slab 11 and Welds to the dummy plug positioned in the exit die 2%. The rolls 2121 are then started to pull the dummy block through the exit die along with the following slab of freshly cast material.

The thickness of the solid layer of barium chloride which provides the retaining surface of my mold is determined and automatically controlled by the rate at which steel is introduced and by the thermal characteristics of the system. Although the surface of the barium chloride layer may be and, I believe, is normally superficially fused, it is at no time completely fused due to the fact that the backing surface is maintained below the melting point of the retaining material.

In this operation I prefer to withdraw heat more rapidly from the bottom of the steel slab through the solid barium chloride to the supporting copper than from its upper surface and thereby cause it to freeze from its lower side, since this avoids the formation of blow holes in the slab. To avoid any premature surface freezing of the slab, I may at times supply .heat to the molten barium chloride 16, although this is usually not necessary, since the incoming molten steel normally provides adequate heat for this purpose.

In my US. Patent 2,754,559 issued July 17, 1956, I have described a method for the casting of fusible materials in which the mold is formed by liquids which are immiscible with one another and with the liquid being cast. In that casting procedure one of the mold liquids used has a higher specific gravity than the fused material being cast while the other has a lower specific gravity than the material, and the fused material is solified while floating between the two mold liquids. By that method I may for example, cast slabs of steel while using molten lead as my heavy mold liquid and fused barium chloride as my light mold liquid.

Under some conditions of operation in accordance with the invention disclosed in U.S. 2,754,559 I have found that the heavy mold liquid has a tendency to become dispersed in the fused material being cast in the form of minute globules or droplets. In some cases, this is an advantageous feature of that method in that it produces a casting having highly desirable properties. Thus, for example, the dispersion of fine globules of lead in steel is desirable since it improves the machinability of the steel. In other cases, it is desirable to avoid such dispersion of the heavy mold liquid in the fused material being cast. This can be done in that method by avoiding turbulence of the mold liquids and by careful control of other variables in the process.

A combination of the present invention with that disclosed by U.S. 2,754,559 provides an alternative way in which to avoid any dispersion of the heavy mold liquid in the fused material being cast, and at the same time enables me to use a shorter mold or to increase the rate of casting, when casting in a continuous manner. The manner in which I accomplish this will be fully explained with reference to FIGURE 4.

Referring specifically to FIGURE 4, it will be seen that the apparatus there illustrated is generally similar to that described above with reference to FIGURES 2 and 3. It differs from that apparatus in having the combination of the entrance conduit 17, gate valve 18, and header 19, at a slightly higher level than the exit die 20. The dilference in level is somewhat exaggerated in the figure for the purpose of clarity. It also dilfers in that the overall mold comprises a first section in similarity to that illustrated by FIGURES 2 and 3 and a second section consisting of a light and a heavy mold liquid of the types described by US. 2,754,559.

The first section of the mold illustrated by FIGURE 4 comprises a copper slab 30 provided with conduits 3131 adapted for the circulation of a cooling fluid from a source not shown by the drawing. The upper surface 32 of the copper slab 30, slopes downwardly in the direction of travel of the molten steel and carries on its surface a layer of 33 solid barium chloride during the casting operation.

In the second section of the mold comprises a lower body of a liquid mold material 34, having a higher specific gravity than the fused material which is being cast. In the casting of steel, this mold liquid 34, may be, for example, molten lead. This fused mold material has immersed therein conduits 3535 for the circulation of a cooling or a heating fiuid as may be required. The upper surface of the mold liquid 34 is level with the lower end of the sloping upper surface of the barium chloride layer 33. This second section of the mold also has an upper body of a liquid mold material 36 which has a lower specific gravity than the fused material being cast, and which is of the same chemical composition as the retaining material 32, i.e. fused barium chloride in this particular case. This body of fused barium chloride extends the length of the tank It) and therefore over the first mold section, as well as forming the upper mold liquid of the second section.

In starting a continuous casting operation utilizing the apparatus illustrated by FIGURE 4, a dummy block is positioned in the exit die 26 with a slablike extension between the traction rolls 21, 21. Molten lead 34 may be introduced into the tank before after the dummy block is placed in position, while exercising care to assure that its upper level is slightly above the lower end of the sloping surface 32 of the copper slab 3i). Fused barium chloride is then introduced into the container 10 through the conduit 22 to cover both the surface of the molten lead 34 and the copper surface 32.

The circulation of a coolant through conduits 3131 is then started and the temperature of the sloping surface 33 reduced below the freezing point of the barium chloride. A solid layer of barium chloride is allowed to form on the cooled surface 33 which has a thickness equal to or in excess of the thickness at which it will be maintained during steady conditions of operating the continuous casting process. Molten steel is then introduced into the header 19 from the conduit 17 by opening the gate valve 18 permitted to fiow downwardly over the slope 32, along the interface between the molten lead 34 and the molten barium chloride 36 and to Weld itself to the end of the dummy block as it is cooled. The traction rolls 21, 21 are then started to withdraw the dummy block and the trailing slab of newly solidified steel through the die 20.

In steady operation, the rate of cooling of the molten steel by the cooled, sloping surface of solid barium 33 is adjusted by the flow of coolant through the conduits 31-31 to cause the steel to form a lower, solid skin before it reaches the surface of the body of molten lead 34. This lower solid skin of steel prevents any admixture of the lead with the still molten core of the ingot after the steel passes off of the surface 34. In completing the solidification of the slab I prefer to freeze it from the bottom upwardly to avoid the formation of internal shrink holes, as in the case of the operation of the mold described hereinbefore with refernce to FIGURE 3.

FIGURE 5, illustrates a casting mold and associated apparatus for the continuous casting of metal in an upwardly direction by the method of this invention. Referring specifically to that figure the numeral 41 designates a tundish from which molten steel can be poured in an accurately controllable stream into receptacle 42. The receptacle 42 is thermally insulated and provided with heating means, such as, for example, an electrical resistance winding 43. The receptacle 42 acts as a hy draulic leg and is connected by a thermally insulated conduit 44 to the bottom of the casting mold designated generally by the numeral 45.

The mold 45 consists of a lower section 46 and an upper section 47. The lower section 46 consists of an inner shell 48 and an outer shell 49 spaced apart to form a coolant chamber 50 which is closed at its upper and lower ends by the end sections 51 and 52, respectively. The inner shell 48 is made of copper, while the outer shell 49 may be made of any structural metal. The outer shell 49 is provided with inlet and exit conduits 53 and 54, respectively, through which a coolant, such as, for example, water is circulated through chamber 50 to cool the copper shell 48. The chamber 50 may, if desired, be provided with suitable bafiles to direct the flow of the coolant to insure uniform cooling of the copper shell 48.

The inner surface of the copper shell 48 carries a solid layer of barium chloride 55 the thickness of which is automatically adjusted by the conditions under which the mold is used in a continuous casting operation as explained hereinbefore with reference to the Equations I and II. The inner surface of the solid barium chloride liner 55 has in cross-section, the shape desired for the cross-section of the casting which is formed in and by the mold. This shape is controlled by the shape of the inner surface of the copper shell 48 and can be varied widely and be complex to produce delicate molding of the casting.

The upper section 47 of the casting mold consists of a chamber 55a, containing molten barium chloride 56 which is an enlarged continuation of the channel formed by the copper shell 48. The cooling or heating coil 57, is adapted to carry a circulating stream of a coolant or a heating fluid to control the temperature of molten barium chloride within the chamber 55a. The chamber 55a is provided with an inlet and exit conduit 58 for molten barium chloride.

The lower end of the mold channel formed by the copper shell 48 and the layer of solid barium chloride id 55 which it carries, is closed by a bottom section 59, through which passes the molten metal conduit 44.

Two pairs of friction rolls 60, 60 and 61, 61 are posi tioned directly above the mold channel formed by the barium chloride layer 55, with their hips aligned with the axis of the mold channel. These rolls are provided with synchronized variable speed drives and are vertically spaced apart a distance which will permit the cutting, for example, by a flame as it passes from the lower to the upper pair of rolls.

To start continuous casting of metal by the use of the apparatus illustrated by FIGURE 5, molten metal is poured into the receptacle 42 until it raises to the end of the conduit 44 at the point at which it enters the mold section 46. The copper shell 48 and the chamber 55a is then filled through conduit 58 with molten barium chloride and coolant is circulated through the chamber 50 to cause barium chloride to freeze on the inner surface of the copper shell 48 and thereby form the solid barium chloride liner 55.

Molten metal is then continuously poured into the receptacle 42 at a uniformly controlled rate. I prefer to utilize under-pouring in which the metal is tapped from the bottom of molten metal in the tundish 41 and introduced into the mold by means of a tubular duct, since it insures a casting free of slag inclusions and delivers the metal to the receptacle 4?. with very little turbulence and minimized metal oxidation to further protect the metal from oxidation, I prefer to maintain a reducing atmosphere over the furnace pouring spout, tundish 41 and receptacle 42.

The circulation of the coolant through the chamber 50 withdraws heat from the copper shell 4-8, from the internal lining layer of solid barium chloride and from the molten metal. The rapid withdrawal of heat from the layer of solid barium chloride prevents its complete fusion by the heat from the molten metal and the withdrawal of heat from the molten metal causes it to form a skin of frozen metal over its surface which progressively thickens and tends to pull away from the surface of the solid barium chloride as the metal moves upwardly through the mold. As the casting shrinks in moving upwardly through the mold, the layer of frozen barium chloride thickens since there is a lessening of the thermal contact between its surface and that of the moving casting until its thickness reaches a point such that no further increase can occur due to a reduction of the rate of heat transfer through the solid film. At this point, the molten barium chloride fills the void between the moving casting and maintains effective heat transfer. This also maintains a solid and thin liquid support for the surface of the moving casting and avoids any localized remelting of the frozen shell which has heretofore created serious difficulties in continuous casting operations of this general ype.

The outer shell of the casting continues to thicken as it passes upwardly through the molten barium chloride, while good thermal contact is maintained at the solidliquid interface between the solid outer surface of the casting and the molten barium chloride. Upon emerging from the mold, the casting passes through the nip of the driven friction rolls 60, 69 and then through the nip of the friction rolls 61, 61. If desired, the casting may be subjected to further cooling between the point at which it leaves the molten barium chloride 56 and the point at which it enters the nip of the rolls 6t), 60 as for example, by an air blast or a spray of a liquid coolant, such as, for example, water. When the casting has reached the desired length in passing through the nip of the rolls 61, 61 it is cut between the rolls, for example, by the known flame cutting technique in which a torch assembly is attached to the moving casting.

In this operation, the rate at which molten metal is poured into the receptacle 42 and the speed of the friction rolls are kept in balance to maintain a substantially 20 constant liquid level in the receptacle 42. This constant liquid level maintains a uniform hydrostatic pressure on the metal passing through conduit 44 and a uniform rate of delivery of the molten metal at the bottom of the mold 45.

In the operation of this apparatus, the temperature of the steel entering the mold 45, and the rate at which heat is withdrawn from copper shell 48 are kept in balance so that the inside of the copper shell is at all times coated with a solid layer of barium chloride. This solid layer barium chloride acts to protect the copper shell from melting and offers the numerous other advantages described elsewhere in this specification.

FIGURE 6 illustrates apparatus which includes a casting mold around which molten steel is cast. In the apparatus illustrated by that figure, which is specifically adapted for the casting of a seamless tube blank, the numeral 7%) designates a tank of a refractory material containing a body of molten steel 71 on which is super imposed a body of molten barium chloride 72. The copper tube 73 is connected at its ends to the inlet conduit 74, and exit conduit by the detachable fittings 76, 76. The conduits 74 and 75 are connected by flexible conduits 77, 77 to a suitable source for a circulating coolant, and are made of a refractory ceramic material. The ends of the conduits 74 and 75' adjacent the copper tube 73 are positioned around the fittings 76, 76 to prevent the solidification of the molten steel on them, which would prevent their detachment from the copper tube 73 at the end of the casting operation. The copper tube 73 which forms the supporting material of this mold carries on its outer surface a solid layer 78 of barium chloride.

The assembly of the copper tube 73, its inlet and exit conduits 74 and 75 and the fitting 76, 76 are carried by a suitable mechanism (not shown by the drawing) which is adapted to raise and lower the assembly or a multiplicity of such assemblies into and out of the position illustrated by the drawing. Any one of a wide variety of conventional mechanisms may be used for this purpose.

In the operation of this apparatus the copper tube 73, with a coolant circulating through it and the assembly associated therewith are lowered through the layer of molten barium chloride and into the body of molten steel. As the cooled tube passes through the molten barium chloride, the layer 78 of the barium chloride solidifies on the copper to form the retaining surface of the mold. Upon immersion of the copper tube 73 with its retaining layer of barium chloride on its outer surface in the molten steel, the steel solidifies in a layer 79 on the retaining surface provided by the solid barium layer 78. During the immersion of this assembly in the molten steel 71, molten steel does not solidify on ceramic conduits '74 and 75 since the ceramic material is a poor conductor of heat which insulates the molten steel from the circulating coolant.

After the desired thickness of steel 79 has solidified on the barium chloride layer '77, the assembly is withdrawn from the molten steel 71 through the molten salt and the circulation of the coolant may be interrupted to permit the residual heat in the solidified steel 79 to fuse the barium chloride layer 78 and the copper. Alternatively, the assembly may be permitted to cool and reheated above the melting point of the barium chloride. In either case, the fittings 76, 76 are then detached from the copper tube 73 which is then withdrawn from the surrounding tube 79 of steel while the intermediate layer of barium chloride is in a molten state. The copper tube can be readily withdrawn since the fused barium chloride acts as a lubricant between the surfaces of the steel and the copper.

The apparatus illustrated by FIGURE 7, like that of FIGURE 6, is adapted for the casting of a seamless tube or tube blank. The tube or tube blank cast by the use of this apparatus differs from that cast by the use of the apparatus of FIGURE 6 in that it has one closed end. Referring specifically to FIGURE 7, it will be seen that the apparatus comprises a tank 80 of a refractory material, which contains a relatively deep body of molten steel 81 and a more shallow layer of molten barium chloride 82.

The mold of this apparatus consists of a copper cylinder 83, which carries on its outer surface a layer of solid barium chloride 84. The lower end of the copper cylinder 83 is closed and it is provided with an inner concentric tube 85 of copper or some other structural metal. The upper end of the concentric tube 85 is connected by a flexible hose 86 with a suitable source for a circulating coolant 87, while the upper end of the annular chamber 88 between the inner wall of the copper cylinder 83 and the concentric tube 85 is closed and connected with a flexible hose 89 through which the circulating coolant can pass out of the concentric tube 85.

This apparatus is provided with a suitable mechanism, not shown by the drawing, for raising the copper cylinder 83 to remove it to a position outside the tank 80 and to return it to the position shown by FIGURE 7. The container 80 is provided with a source of heat to maintain the molten steel 81 in a molten condition, such as, for example, an insulated electrical resistance heating element 90 as shown by the figure.

In the operation of the apparatus illustrated by FIG- URE 7, the circulation of a fluid coolant 37 within the copper cylinder 83 is started by passing the coolant through the flexible tube 86, into the inner concentric tube 85, through the annular chamber 83 and out through the flexible tube 87, while the cylinder 83 is outside the container 80. After the copper cylinder 83 has been cooled it is lowered into the container 80 to the position shown by FIGURE 7.

As the copper cylinder 83 passes through the molten barium chloride 82, a layer of solid barium chloride 84 freezes on its lower end and outer cylindrical surface, and forms a retaining layer to protect the copper from fusion by the heat of the molten steel. As the copper cylinder 83 with its outer layer 84-, of solid barium chloride passes downwardly into the molten steel 81, the steel solidifies on the outer surface of the solid barium chloride 84 in the form of a cylinder 01 having a closed end 92.

When the thickness of the solid steel cylinder 91 reaches the desired point, the copper cylinder 83 and the layers of barium chloride $4 and steel 01 and 92 which it carries on its outer surfaces, are raised to separate them from the molten steel 81 and the molten barium chloride 82. As the outer surfaces of the steel 91 and 92 pass through the molten barium chloride 82, they become coated with a fiuid layer of barium chloride which protects the steel surfaces from atmospheric oxidation.

After the assembly of the copper cylinder 84 and its outer layers of solid barium chloride 84 and solid steel 91 and 92 are outside the tank 80, the steel cylinder 91 may be slipped off of the copper cylinder 84 by interrupting the flow of the fluid coolant 87 to permit the residual heat in the solid steel to fuse the barium chloride 84. Alternatively, the assembly may be permitted to cool and at a later time be reheated to a temperature above the melting point of the barium chloride to permit the steel cylinder to be readily separated from the copper cylinder 83.

Although FIGURE 7 illustrates the copper cylinder 83 with its axis in a vertical position, it is not necessary that it be in this position during the casting operation. If it is desired to use a more shallow body of molten steel 81 than that required for the vertical positioning of the copper cylinder 83, the cylinder can be inserted into the molten barium chloride 82 and molten steel 81 at an oblique angle.

Both FIGURES 6 and 7, for the purpose of simplicity,

illustrate the formation of a single casting in each operation. It will be appreciated that any number of tube blanks can be cast in the operation described with reference to FIGURE 6 by providing a plurality of copper tubes 73, and associated parts and lowering them simultaneously into the bodies of molten barium chloride and molten steel and then separating them therefrom. Similarly, the operation described with reference to FIGURE 7 can be carried out to cast simultaneously a plurality of closed end tubes by providing any desired plurality of copper tubes 03 and lowering them simultaneously into the fused barium chloride and fused steel and then removing them therefrom.

Both FIGURES 6 and 7 illustrate my preferred procedure in locating the molten barium chloride on the molten steel, since the molten barium chloride protects the steel from atmospheric oxidation. However, this location of the barium chloride or other fused retaining material is not an essential feature of my method. The molten retaining material may be located in a separate container and the assembly carrying the backing material of the mold dipped first into the fused retaining material and then into fused material which is to be cast.

FIGURE 8 illustrates a mold in accordance with this invention which is adapted for the continuous casting of sheet steel in a highly efiicient manner. Referring specifically to that figure, the numeral designates a tank of a refractory material which is provided with a supply of heat, as for example, an insulated electrical resistance heating unit 101. The tank 100 contains a body of molten steel 102, carrying on its upper surface a superimposed body of fused barium chloride 103.

The hollow drum 104 has a cylindrical surface made of copper and a hollow drive shaft. It is provided with a source of rotary power and a mechanism for lowering it to the position shown by FIGURE 8 and for raising it from that position to a position in which the periphery of the drum 104 is above the surface of the fused barium chloride 103.

The hollow drive shaft of the hollow drum 104 is connected by conduits to a suitable source for the circulation of a fluid coolant to and from the interior of the drum 104, to provide a circulating body 105 of coolant liquid within the interior of the drum 19 2. The interior cylindrical surface of the drum 104i is preferably provided with vanes 100-106 which, during the rotation of the drum, propel the coolant liquid 105 against the inner cylindrical surface of the drum. The circulating body of coolant 105 within the drum 104 fills the drum to a horizontal level well above the surface of the fused body of barium chloride 103 and the remaining upper interior space within the drum 104 is filled by a body 107 of a compressed gas, such as, for example, air.

One of the ends of the drum 104 is provided with a relief valve for the venting of gas from the interior of the drum to adjust the space occupied by the body of compressed gas 107. The drum 104 has ends which have low heat conductivity. These ends may be made, for example, of a refractory ceramic material or of an outer surface of a refractory metal having a melting point above the temperature of the molten steel 102, an intermediate layer of an insulating material and an inner layer of a material which is impervious to the coolant liquid.

The scraper bar 108 extends across the width of the circumferential face of the drum 104. This scraper bar 108 is provided with a source of heat which is capable of maintaining it at a temperature above the melting point of barium chloride. At least the outer surfaces of the scraper bar 108 are made of a material which is a good conductor of heat and as will be brought out hereinafter in describing the operation of this apparatus, the quantity of heat which must be furnished to this bar 108, once it is heated to a tempereature above the melting point of the barium chloride is rather small, if any is required.

In starting the operation of the apparatus illustrated 23 by FIGURE 8, the bodies of molten steel 102 and of molten barium chloride 103 are positioned in the tank 100 while the drum 194 and its associated mechanism are in an elevated position, above the level which the surface of the molten barium chloride 103 seeks in the tank 109. The circulation of the coolant 195 is started within the drum 194, while adjusting the volume of the body of compressed gas 107 within the drum. The rotation of the drum 184 is, preferably then started and the rotating drum lowered to its operating position. As the chilled circumferential surface of the drum 1114 passes through the layer of fused barium chloride 103, a solid layer of barium chloride 110 is frozen on the cooled copper surface. As this layer of solid barium chloride passes into the molten steel, solid steel is frozen on its surface as a layer 111.

As the drum 104 is rotated the segment of its surface below the upper surface of the body of molten steel 1&2 builds up a layer of solid steel 111 which is carried through the molten barium chloride 103 and is subsequently protected from atmospheric oxidation by a film of molten barium chloride 112 which it retains on its outer surface.

The scraper bar 198 directs the sheet of steel 111 away from the periphery of the drum 1&4. The partial or complete fusion of the barium chloride 11h leaves a residual layer 113 of fluid barium chloride on the lower surface of the steel sheet 111 to protect it from atmospheric oxidation. At the same time the fused barium chloride acts as a lubricant for the surface of the scraper bar 198. In steady operation, little or no heat is required to maintain the temperature of the scraper bar 193 above the melting point of barium chloride.

After passing over the scraper bar 108 the sheet of steel may be further cooled by air blasts, water sprays or both and the residual barium chloride 112 and 113 removed from its surfaces by the action of, for example, water sprays, water-wet revolving brushes or the like.

The gauge of the steel sheet produced by this apparatus depends upon the circumference of the drum 104, its speed of rotation and the thermodynamic conditions of the operation. Under steady conditions of continuous operation this gauge can be controlled with a surprising degree of accuracy. Furthermore, the sheet produced is highly uniform and free of defects because of the fact that it is frozen entirely from one side, i.e. the side adjacent the solid barium chloride retaining surface of the mold.

The disposition of the sheet 111 after it has been cooled and freed of its surface films 112 and 113 of barium chloride, depends upon its thickness. In the production of sheets, which are thin enough to be flexible at ambient temperatures, the sheet may be wound in a coil on a mandrel driven at speeds progressively synchronized to coil the sheet at the same rate at that at which it leaves the scraper bar 108. In the production of sheets having a thickness such that they are not sufficiently flexible to permit them to be coiled, the sheet may be periodically cut into lengths by known techniques, such as, for example, by the use of a cutting torch which travels with the sheet while cutting it laterally.

The method in accordance with this invention is adapted for the production of castings from a plurality of different metals. In the case of the apparatus illustrated by FIGURE 1, a bimetallic ingot may be produced by partially filling the container 1, with one metal, causing it to solidify and then adding a second metal. Similarly in the case of the apparatus illustrated by FIGURES 2 and 3, one sheet or slab of metal may be solidified and then a second metal poured on top of the solidified slab. Again in the case of the forms of apparatus illustrated by FIGURES 6 and 7, respectively, a second metal can be cast on the first metal cast by introducing the mold assembly into a second bath of the second molten metal after the first layer of metal has been solidified on the mold as illustrated. In this manner a bimetallic tube or tube blank may be produced.

Referring specifically to FIGURE 9, the numeral 121) designates a copper container which carries on its inside surfaces a layer of solid barium chloride 122, which provides a retaining surface for molten steel 123, within the cavity of the mold. The weight of copper in the copper container 121 is at least 2.2 pounds for each pound of steel 123 within the mold, as required by the thermodynamic relationships of the mold, as shown by Example 4 given hereinbefore.

In carrying out the method in accordance with this invention, by the use of the simple mold illustrated by FIGURE 9, I first introduce the molten barium chloride into the copper container 120, solidify the barium chloride on the bottom and side surfaces of the inside of the container and pour off any excess molten barium chloride, to form a layer of solidified barium chloride which is preferably slightly thicker than the layer 122 of solid barium chloride, forming a part of the mold as the ingot 123 is actually solidified. I then pour molten steel into this barium chloride-copper mold and merely allow the steel 123 to solidify to a solid ingot. After the steel 123 has solidified at least to an extent such that it can be handled, and while it is still at a temperature above the melting point of the barium chloride, the casting is removed from the mold. Alternatively, the mold and its contents may be permitted to cool and then be reheated above the melting point of the barium chloride retaining layer. In either case, the superficial layer of molten barium chloride adjacent the ingot permits it to be readily removed from the mold.

In carrying out this molding procedure, the thickness of the layer 122 of solid barium chloride which forms an essential part of the mold is automatically adjusted by the thermal characteristics of the system. Any excess barium chloride which is initially placed on the inside of the copper container is fused by the heat of the molten steel, and by virtue of the fact that its specific gravity is lower than that of steel, the excess barium chloride which is fused is forced to the surface of the steel, leaving the solid layer of barium chloride of automatically adjusted thickness on the inside surface of the copper container. The fused surface layer of barium chloride protects the steel from atmospheric oxidation.

FIGURES 10 and 11 illustrate the application of the method in accordance with this invention in a procedure in which steel is cast on the outside of a barium chloridecopper mold to produce a seamless tube, tube blank, or hollow cylinder of steel. Referring specifically to FIG- URE 10, the numeral 125 designates a refractory container which contains a body of molten steel 126 on which is resting at body of molten barium chloride 127. In the casting operation, a solid, cylindrical rod 128 of copper, suspended on steel ropes or chains 129, 129 is lowered rapidly through the layer of barium chloride 127 into the body of molten steel 126, and then withdrawn therefrom after a period of time which permits the solidification of a shell of steel on the cylindrical rod of copper. As the cylindrical rod of copper 128 is lowered through the layer 127, of barium chloride, a layer of barium chloride 131 is solidified on its surface due to the absorption of heat from the molten barium chloride by the copper. This forms a mold, in accordance with this invention, consisting of the solid copper backing cylinder 128, coated on all surfaces with a film or layer of solid barium chloride 131.

While in the body of molten steel 126, the copper cylinder 128 withdraws heat through the layer of barium chloride 131 and solidifies a layer of solid steel 132 on the outer surfaces of the barium chloride retaining material. The mold is then withdrawn from the molten steel as soon as the desired thickness of steel is deposited on its surface. The time over and during which the mold, consisting of the copper 128 and the solid layer of barium chloride 131 is permitted to remain in the molten steel depends upon the temperature of the molten steel and the thickness desired in the casting. Conversely, the time during which the mold is immersed in the molten steel is used to control the thickness of the walls of the hollow cylindrical casting produced by the operation. In any case, as shown by the computation illustrated by Example 4, not more than 0.45 pounds of steel can be deposited on the copper cylinder for each pound of copper thereof.

As shown by FIGURE 11, when the mold is withdrawn from the molten bath 126 of steel, it consists of the solid copper cylinder 128, an intervening layer of barium chloride 131 and a hollow cylinder of steel 132 superimposed on the barium chloride. The layer of barium chloride 131 consists of a solid layer of barium chloride adjacent to the surface of the copper cylinder 128, surrounded by a film of molten barium chloride adjacent to the inner surface of the solidified steel, as long as the copper cylinder 128 is still absorbing heat and below the melting point of barium chloride.

In carrying out this operation, I follow the thermal conditions shown by Example 6 and withdraw the solid cylinder 128, of copper from the shell of steel 132 before the temperature of the assembly drops to a point such that the entire layer of barium chloride 1131 becomes solidified. The presence of the liquid barium chloride simplifies the matter of removing the solid cylinder 128 of copper from the shell 132 of steel.

As will be fully appreciated by reference to Example 8 given hereinbefore, I may use the foregoing procedure to produce seamless tubes, tube blanks or hollow cylinders, merely by the substitution of a molten bath of copper for the molten steel 126 of FIGURE 9, and by making the proper adjustments in the temperatures utilized and in the time of immersion of the mold in the molten copper, as indicated by Equations I, II, and III given above.

From a practical standpoint, the method and the casting mold, in accordance with this invention, offers a variety of advantages. The high thermal conductivity of the supporting material permits the rapid removal of large quantities of heat from the material being cast, while the low thermal conductivity of the retaining surface layer causes that layer to act as a buffer to protect the backing surface and to insure a uniform, steady removal of heat from the casting. This steady, uniform and rapid removal of heat causes the casting to solidify uniformly from all surfaces in contact with the mold to produce a casting of uniform structure. The rate at which the casting operation can be carried out can be materially increased while producing castings of superior quality due to the rapid removal of heat by the backing material.

It has been noted hereinbefore, that the layer of retaining material of the mold may undergo superficial melting but cannot be melted all the way through to the backing material when operating in accordance with this invention. This tendency to superficial melting is definitely advantageous in that it keeps the casting in good thermal contact and avoids the formation of an air gap between the casting and the mold due to the shrinkage of the casting, such as frequently occurs in the conventional casting procedures. Furthermore, the formation of the liquid layer of barium chloride permits the ready removal of the casting from the mold surface.

Another definite advantage of this invention arises from the fact that the backing solid of the mold is protected from wear by the layer of the retaining material which is readily renewed, and in fact, is usually renewed prior to each casting operation. Still another advantage of this invention arises from the fact that the retaining material may be fused after the casting is formed by the residual heat of the casting, since such fusion of the layer of retaining material permits the casting to be easily separated from the supporting material of the mold. This fusible material is cast around the mold, as, for example, in the production of seamless tubing as described hereinbefore with reference to the drawings. In such an operation, the melting of the layer of retaining material, for example,

barium chloride, both in providing a clearance between the inside of the casting and the backing material of the mold and in acting as a lubricant between the solid surfaces, permits the backing material of the mold to be readily withdrawn from the casting.

Another major advantage provided by the method and apparatus of this invention arises in operations using a massive mold in which the fusible material is cast around the mold, arising from the fact that the mold requires no circulating coolant during the casting operation. This avoids the use of cumbersome apparatus and avoids thermal problems which are sometimes impossible to solve in practical operations.

In casting a fusible material arround either the massive type or the fluid-cooled type of mold in accordance with this invention, the metal solidifies outwardly from the mold and does not entrap dissolved gas which would form voids in the casting as it comes out of solution. As the metal solidifies the dissolved gases remain in the fused metal with the result that the cast metal is free of the troublesome voids which are usual in meal castings. This avoidance of voids is another major advantage of this invention.

In the foregoing, I have given numerous details as to the manner in which this invention can be carried out and have disclosed numerous combinations of materials for use as casting molds in accordance with this invention. I have specifically exemplified a number of different casting operations and described with reference to the drawings the use of two different specific embodiments of the mold and the method in accordance with this invention. It will be fully understood that the details I have given have been for the purpose of fully disclosing and illustrating the invention, and that many different forms of molds and many substitutions of materials and variations in the details of the casting procedures described can be made without departing from the spirit of my invention or the scope of the claims which follow.

This application is a continuation-in-part of my copending applications, Serial No. 629,590, filed December 20, 1956, and Serial No. 671,029, filed July 10, 1957 both of which are abandoned.

I claim:

1. A method for the casting of tubes of a fusible material which consists essentially of lowering through a molten body of a retaining material which has a low thermal conductivity when in the solid phase, and which is immiscible with and has a lower specific gravity than the fused material to be cast, and into a molten body of the fusible material to be cast on which the said molten body of retaining material is floating, an assembly consisting essentially of a horizontally positioned tube of a backing material which has high thermal conductivity and has inlet and exit conduits of a refractory material and which has a low thermal conductivity (letachably attached to its respective ends which extend upwardly from the said tube and are attached by flexible inlet and outlet conduits through which a cooling fluid is being circulated into and out of the said tube of supporting material to lower its surface to a temperature below the freezing point of the said retaining material and causes a layer of retaining material to freeze on the outer surface of the supporting tube; retaining the said tube of sup porting material, with its covering of retaining material within the said molten body of fusible material for the period of time required for a desired thickness of the fusible material to freeze on the outer surface of the said retaining material; raising the said assembly and the frozen cylinder of fusible material out of the said molten bodies; terminating the circulation of the said coolant; removing the detachable end conduits from the said supporting tube and removing the solid cylinder of cast fusible material from the said cylinder of supporting material.

2. A method for the casting of seamless tube blanks which consists essentially of lowering through a molten 2? body of barium chloride floating on a molten body of steel and into the body of molten steel on which the molten body of barium chloride is floating, an assembly consisting essentially of a horizontally positioned sup porting tube of a material selected from the group of materials consisting of copper and copper alloys which has inlet and exit conduits of a refractory material which has a low thermal conductivity detachably attached to its respective ends and extending upwardly from the said tube and are attached by flexible inlet and outlet conduits through which a cooling fluid is being circulated into and out of the said tube of supporting material to lower its outer surface to a temperature below the freezing point of the barium chloride and causes a layer of the barium chloride to freeze on the outer surface of the supporting tube; retaining the supporting tube with its covering of retaining material within the said body of molten steel for the period of time required for a desired thickness of the steel to freeze on the outer surface of the barium chloride; raising the said assembly and the solid cylinder of steel out of the said molten bodies; terminating the circulation of the said coolant; removing the detachable end conduits from the said supporting tube, terminating the circulation of the said coolant; removing the detachable end conduits from the said supporting tube and removing the steel cylinder from the supporting tube.

3. A method for for casting tubes of a fusible material which consists essentially of lowering through a molten body of a retaining material which has a low thermal conductivity when in the solid phase and which is immiscible with and has a lower specific gravity and melting point than the fused material to be cast and is floating on a molten body of the fusible material to be cast, and into the said molten body of the fusible material, an assembly consisting essentially of an outer, vertically positioned tube having a closed lower end, an inner concentric tube which has an open end positioned within and near the closed end of the outer tube, at least the outer tube of which is made of a backing material which has high thermal conductivity, inlet and outlet conduits from which a coolant liquid is circulating through the inner tube and the annular space between the two tubes, which are connected at the upper ends of the said concentric tubes, and flexible conduits connecting the said inlet and exit conduits, respectively, to the source of the circulating coolant liquid, while maintaining the outer surface of the outer tube of the assembly at a temperature below the melting point of the said retaining material and of the said fusible material by the said circulating coolant; retaining a substantial length of the outer tube of the said assembly Within the molten body of the fusible material for a period of time which permits the freezing of a layer of the solid fusible material in the form of a closed end cylinder of the desired thickness on the solid layer of retaining material which was frozen on the outer surface of the outer tube when passing through the molten retaining material; raising the said assembly to remove the said tubes from the said molten bodies, terminating the circulation of the coolant, and removing the frozen, closed end cylinder of fusible material from said assembly.

4. A method for the casting of seamless steel tube blanks which consists essentially of lowering through a body of molten barium chloride which is floating on a body of molten steel and into the molten steel, an assembly consisting of an outer vertically positioned copper tube having a closed lower end, an inner concentric tube which has an open end positioned within and near the closed end of the outer tube, inlet and outlet con duits from which a coolant liquid is circulating through the inner tube and the annular space between the two tubes, which are connected at the upper ends of the said concentric tubes and flexible conduits connecting the said inlet and exit conduits to the source of the circulating coolant liquid while maintaining the outer surface of the outer tube of the assembly at a temperature below the melting point of the barium chloride and of the steel by the said circulating coolant; retaining a substantial length of the said assembly within the molten steel for a period of time which permits the freezing of a solid layer of steel in the form of a closed end cylinder of the desired thickness on the outer surface of the layer of solid barium chloride which was frozen on the outer surface of the said copper tube as it passed through the molten barium chloride; raising the said assembly to remove the said tube from the molten steel and the molten barium chloride; terminating the circulation of the coolant; and removing the closed end cylinder of steel from the said assembly.

5. A method for the casting of steel which comprises bringing a body of molten steel into contact with the surface of a layer of barium chloride which is supported by the surface of a body of a backing material selected from the group consisting of copper and alloys of copper, which has the capacity to absorb the heat of fusion of the molten steel and any super-heat carried by the molten steel, while maintaining the surface of the said backing material in contact with the solid barium chloride at a temperature below the melting point of the barium chloride, which maintains a solid layer of the barium chloride in contact with the said backing material, while permitting the fusion of a layer thereof adjacent the steel, and permitting the said body of copper to absorb heat from the said molten steel, through the solid layer of barium chloride until at least a portion of the molten steel has solidified, and removing the resulting casting from contact with the barium chloride surface of the said mold.

6. A method for the casting of copper which comprises bringing a body of molten copper into contact with the surface of a layer of barium chloride which is supported by the surface of a body of a backing material selected from the group consisting of copper and alloys of copper, which has the capacity to absorb the heat of fusion of the molten copper and by super-heat carried by the molten copper, while maintaining its surface in contact with the solid barium chloride at a temperature below the melting point of the barium chloride, which maintains a solid layer of the barium chloride in contact with the said backing material, while permitting the fusion of a layer thereof adjacent the copper being cast, and permitting the said body of copper to absorb heat from the said molten copper, through the solid and the liquid layer of barium chloride until at least a portion of the molten copper has solidified; and removing theresulting casting from contact with the barium chloride surface of the said mold.

7. A method for the casting of steel which comprises bringing molten steel into contact with the surface of a layer of barium chloride, which is supported on the surface of solid backing material selected from the group consisting of copper and alloys of copper; Withdrawing heat from the copper and thereby causing heat to flow from the molten steel at a rate which maintains a layer of molten barium chloride adjacent the steel and a solid layer of barium chloride adjacent the said backing material, until the steel is at least partially solidified, thereby keeping a continuous film of barium chloride and all of the backing material in a solid state.

8. A method for the continuous casting of molten steel which comprises flowing a stream of the molten steel over the surface of a layer of barium chloride supported on a solid copper surface, and under a fused layer of 

7. A METHOD FOR THE CASTING OF STEEL WHICH COMPRISES BRINGING MOLTEN STEEL INTO CONTACT WITH THE SURFACE OF A LAYER OF BARIUM CHLORIDE, WHICH IS SUPPORTED ON THE SURFACE OF SOLID BACKING MATERIAL SELECTED FROM THE GROUP CONSISTING OF COPPER AND ALLOYS OF COPPER; WITHDRAWING HEAT FROM THE COPPER AND THEREBY CAUSING HEAT TO FLOW FROM THE MOLTEN STEEL AT A RATE WHICH MAINTAINS A LAYER OF MOLTEN BARIUM CHLORIDE ADJACENT THE STEEL AND A SOLID LAYER OF BARIUM CHLORIDE ADJACENT THE SAID BACKING MATERIAL, UNTIL THE STEEL IS AT LEAST PARTIALLY SOLIDIFIED, THEREBY KEEPING A CONTINUOUS FILM OF BARIUM CHLORIDE AND ALL OF THE BACKING MATERIAL IN A SOLID STATE. 